The Australian Standard AS 1680 suggests lighting levels in an office environment as follows;

"Ordinary" visual tasks should be in range 300 to 400 lux [320 lux (task) and 160 lux (Background)]. Illumination is measured in units of LUX - lumens per square metre

For more demanding visual tasks, including proof reading and working from poor quality photocopies, 600 lux is suitable

Older workers may require stronger lighting

Depending on you type of job, the amount of light you need varies. After finding a comfortable light level for your office you can start to choose between direct or tracking lighting. The tracking lighting makes the ambient much more comfortable (in my opinion).